Written by Benoit Mortgat who has also kindly provided a zip file containing both a bash module and a PowerShell module. These can be loaded as part of your startup profile making them easily available.
Also available on GitHub, pull requests are welcome.

Examples:

$ strongpw paypal
Encryption key:
5h8RDZxO6xyXbaLrxKE6

Security

Command-line scripts can be an aid to cracking passwords. If you enter a password into a website which saves the password as plain text (no password hashing) and if that website is subsequently hacked, the attacker would have one of your passwords. The attacker could then run a brute force or dictionary attack through the same hash algorithm until they find a match with the first password, the attacker would then have your master password.

The way to protect yourself against this type of attack is to ensure that your Master Password is long enough (with enough entropy) that such an attack would take an impractical length of time to complete.